Turns the picture into a raised relief, as though it were stamped into metal.
The method is a lopsided comparison. Each pixel is compared with its neighbours, but weighted so one diagonal counts positively and the opposite one negatively. Surfaces sloping toward the light come out bright, surfaces sloping away come out dark, and anything flat cancels to nothing, which is why an embossed picture is mostly mid grey with detail only at the edges.
angle moves the light around. It does that by rotating which neighbours get compared rather than by changing the weights, so the character of the relief stays the same at every angle.
style picks between keeping the picture's colours in the relief, or converting to neutral grey and adding a little colour back only near the edges, which gives the classic carved-stone look.